DMX sounds pretty cool:
Xdmx is proxy X server that provides multi-head support for multiple displays attached to different machines (each of which is running a typical X server). When Xinerama is used with Xdmx, the multiple displays on multiple machines are presented to the user as a single unified screen.So basically you can hook up other computers and have their displays used as if they were attached via another video card to your computer.
Personally I like my dual monitor + (dual) KVM so I can have two monitors and use them both in both windows and linux, but hey, this lets you use your spare laptop (or two) as an extra part of a screen :) From the slashdot article about dual monitors.
Posted by Arcterex at October 18, 2004 12:20 PM
Sounds a lot like x2x: http://freshmeat.net/projects/x2x/
Cool, this is way better then x2x - this will let you do stuff like drag applications between the displays as well, or maximize an application across multiple displays that are attached to multiple machines.
IF this handles machines appearing and disappearing gracefully enough then this would be great for such as using your laptop next to your normal desktop machine when it's there.
Of course the ultimate would be a multi-platform version of this that'd let you have a unix box and a windows box display applications on each others screens as well, but that'd be way too much work. Next best thing would be running a DMX enabled X on the windows box, so at least your X apps could use both screens.